The present invention relates to a novel radiation curable or -crosslinkable polymeric composition or, more particularly, to a novel radiation curable or crosslinkable polymeric composition comprising a specific organopolysiloxane, which is suitable to form, with a relatively small dose of irradiation with a radiation such as electron beams, a cured surface film on a substrate surface having releasability against adhesives or sticky substances and useful as a back-surface treatment agent of pressure sensitive adhesive tapes or surface treatment agent of release paper for pressure-sensitive adhesive labels and the like, hereinafter referred to as a surface releasing agent.
It is well known that a variety of organopolysiloxanes or compositions thereof are used in the application as a surface-releasing agent, of which organopolysiloxanes having two or more of (meth)acryloxy, i.e. acryloxy or methacryloxy groups in a molecule are widely used as a radiation curable surface-releasing agent (see, for example, Japanese Patent Publication 52-3190) by virtue of their crosslinkability by the irradiation with electron beams. Further, Japanese Patent Publication 53 36515 teaches a radiation curable surface-releasing agent comprising an organopolysiloxane of the above mentioned type and a sensitizer.
Such a (meth)acryloxy-containing organopolysiloxane or a composition based thereon has a problem that the surface-releasability against adhesive materials is necessarily decreased when the density of the (meth)acryloxy groups in the organopolysiloxane is increased with an object to obtain improved radiation crosslinkability. This is presumably due to the great polarity of the (meth)acryloxy groups which is responsible for the increase in the surface tension of the coating agent and the peeling resistance when a pressure-sensitive adhesive tape is applied and bonded to the release-treated surface and then peeled off. This disadvantage can be partly overcome by admixing the (meth)acryloxy containing organopolysiloxane with a dimethylpolysiloxane of a straightly linear molecular structure having a high molecular weight but no radiation-crosslinkability (see, for example, Japanese Patent Publication 62-30234). Though not ineffective in improving the surface releasability, such an organopolysiloxane composition has a problem that the coating film produced by the electron beam irradiation of low dose is poor in respect of the residual adhesiveness. Alternatively, a proposal has been made in Japanese Patent Publication 57 57096 for the combined use of an organopolysiloxane having (meth)acrylox groups and an (meth)acrylate ester compound of a polyhydric alcohol or a (meth)acryloxy-containing organopolysiloxane of a low molecular weight. Such an organopolysiloxane composition, however, is not quite satisfactory as a surface-releasing agent due to the relatively poor releasability characteristics when a coating film thereof is cured by the irradiation with radiations even though satisfactory relative to the radiation curability and the residual adhesiveness.